Newswise — An independent study conducted by Harvard Medical School researchers, published in the July edition of the International Journal of Obesity, finds that women who were breastfed did not have lower incidence of overweight or obesity in adulthood when compared to women who were not breastfed.

Additionally, the study finds that although exclusive breastfeeding (for at least six months) is associated with leaner body shape at five years, this association does not persist into adolescence or adulthood. The study (available at: http://www.nature.com/ijo/journal/v31/n7/full/0803622a.html) is based on data collected from 35,526 women participating in the Nurse's Health Study II (NHS), is the largest to date examining breastfeeding and its influence on adult weight status.

Study researchers acknowledge that breastfeeding promotes the health of both mother and child but concluded, "it is unlikely to play an important role in controlling the obesity epidemic." According to a recent Associated Press (AP) article, the study's lead author, Karin Michels of Harvard Medical School, stated, "I'm the first to say breast-feeding is good. But I don't think it's the solution to reducing childhood or adult obesity."

Further, the findings of this study contradict conclusions of other previous epidemiologic studies that report a modest protective effect of breastfeeding on the development of adult overweight and obesity. "Many of those [previous] studies," Dr. Michels explained, "failed to properly account for socioeconomic factors that also may have had an influence [on adult weight]."

According to Mardi Mountford, Executive Vice President of the International Formula Council (IFC)*, "This independent study from Harvard does not support an association between breastfeeding and a reduced risk of obesity. If fact, both breastfeeding rates and obesity have increased to record levels in the U.S. over the last 30 years."

Mountford points out that many factors--including caloric intake, physical activity and genetics are involved in establishing and maintaining a healthy weight, adding that "scientific evidence does not show a direct cause and effect relationship between infant feeding and obesity—specifically, no studies have shown that breastfeeding prevents obesity, or conversely that not breastfeeding causes obesity."

In the same journal (July issue of International Journal of Obesity), a separate pediatric review article reinforces the lack of a cause and effect relationship, stating, "Current evidence seems insufficient to demonstrate undoubtedly that programming of obesity occurs during infancy in humans or to support recommendations for obesity prevention starting in infancy. However, as breastfeeding has demonstrated benefits other than obesity prevention, breastfeeding promotion has been recommended as part of the strategy to prevent obesity, despite the lack of experimental evidence."

Another recent study, published in the June 2007 issue of American Journal of Clinical Nutrition, concluded that the protective effect of breastfeeding that some studies have found is likely due to the fact that women who breastfeed their infants also tend to have qualities that make them less likely to raise obese children. (The abstract is available at: http://www.ajcn.org/cgi/content/abstract/85/6/1578.) The researchers studied 4,325 children aged 9 to 10 years old, and used statistical techniques to control for factors linked to both breastfeeding and obesity risk, including mother's education and socioeconomic class, maternal BMI, time the mother spent watching television daily, and time spent in a car for each weekday.

"There are several reasons for why mothers should breastfeed their children, independent of obesity," Dr. Andre M. Toschke of Kings College London, the study's lead author, told Reuters Health on June 29. "(Our) study questions a little bit the argument of breastfeeding for protection against obesity." To eliminate confounding factors in future research, he recommended studies of breastfeeding promotion interventions with adequate follow-up.